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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 44 |
| 3 | 320 |
| 4 | 2328 |
| 5 | 16936 |
| 6 | 123208 |
| 7 | 896328 |
| 8 | 6520712 |
| 9 | 47437640 |
| 10 | 345104904 |
| 11 | 2510609608 |
| 12 | 18264477064 |
| 13 | 132872558664 |
| 14 | 966636864776 |
| 15 | 7032203170760 |
| 16 | 51158695924872 |
| 17 | 372175277815624 |
| 18 | 2707544336559112 |
| 19 | 19697160911545032 |
| 20 | 143295215053933448 |
| 21 | 1042460827200624200 |
[1,6,44,320,2328,16936,123208,896328,6520712, 47437640,345104904,2510609608,18264477064, 132872558664,966636864776,7032203170760, 51158695924872,372175277815624,2707544336559112, 19697160911545032,143295215053933448, 1042460827200624200] |